1. Field of the Invention
This invention relates to a flash photography system for a camera and more particularly to a flash photography system arranged to have the charging voltage of a main capacitor of a flash device automatically controlled according to a guide number in carrying out flash photography.
2. Description of the Related Art
The conventional flash photography system has been arranged to detect the charging voltage level of a main capacitor connected to the flash bulb of a flash device only at a predetermined level and to charge the main capacitor to bring its voltage up to the predetermined level if the level detected is found to be lower than the predetermined level.
Meanwhile, it is known that some of the recent lens-shutter type cameras having the above-stated flash photography system are arranged to automatically correct an aperture value according to a guide number obtained by the flash device of each individual camera, as long as the photo-taking optical system is within an aperture adjustable range in carrying out flash photography.
However, the above-stated known camera and the flash photography system have the following shortcomings.
(i) The electrostatic capacity of the main capacitor of one manufactured flash device differs from that of another, because of a manufacturing tolerance. The guide number of each individual flash device thus differs from that of another in proportion to the square root of the ratio of electrostatic capacity. If different flash devices are mounted on cameras of the same kind, therefore, the guide number of the flash device of one camera differs from that of another as much as a value which is proportional to the square root of the ratio of electrostatic capacity of the main capacitor. However, in the case of the above-stated known lens-shutter type camera, an exposure is decided according to the F-number of the photo-taking optical system and the guide number of the flash device (without correcting the aperture value) if the luminance of the object obtained by light measurement is outside of an aperture adjustable range in the mode of flash photography. Hence, in this instance, an illuminating condition set for one camera becomes different from a condition set for another camera even under the same shooting (photographing) conditions.
(ii) Since the electrostatic capacity of the main capacitor of the flash device varies with changes taking place in ambient temperature, the guide number of the flash device also varies with the ambient temperature. This fact further causes the flash photographing performance of one camera to become different from that of another in addition to the problem mentioned in (i) above.